1. Field of the Invention
This invention relates to primer compositions. In particular, this invention relates to primer compositions which are used for the firm adhesion of room temperature-curable silicone rubbers or room temperature-curable silicone-modified organic rubbers to various types of substrate surfaces with which the silicone rubbers are in contact during the curing.
2. Description of the Prior Art
Today, room temperature vulcanizable silicone rubbers are used in large quantity as a sealing material in buildings because the durability of the rubber itself is far superior to organic rubbers. Room temperature vulcanizable silicone-modified organic rubbers are also used as a sealant for buildings. Because many different materials are used in buildings, it is important that the room temperature vulcanizable silicone rubbers and the room temperature vulcanizable silicone-modified organic rubbers firmly bond to the different substrate materials. The substrates can be, for example, metals such as aluminum, steel, and stainless steel; coated building materials such as aluminum coated with acrylic resin, urethane resin, or epoxy resin; hard inorganic building materials such as glass, tiles, and building stones; and porous inorganic base materials such as mortar, concrete, and ALC. Conventional procedure is to pretreat such substrates with an appropriate primer, designed for the particular substrate, thus many different primers are used. Thereafter room temperature vulcanizable silicone rubber or room temperature vulcanizable silicone-modified organic rubber is applied and a bond is formed during the curing process. However, it is difficult to bond these rubbers to such substrates as pure aluminum, surface-treated aluminum, stainless steel, aluminum coated with various resins, and mortar. Attempts to bond the rubbers to these substrates gives rise to problems, such as deterioration of the rubber and peeling at the interface between the rubber and the substrate. Therefore, primers which can maintain a strong bond strength for a long period, in particular, those which can maintain a strong bond strength for a long period even when immersed in water, are in demand.
The inventors in U.S. patent application, Ser. No. 399,606, filed July 19, 1982, describe single-component type primer compositions comprised of silicone-modified epoxy resins having epoxy groups and silicon-bonded alkoxy groups and organotitanates, said application being hereby incorporated by reference to show the preparation of the silicone-modified epoxy resins. However, when used as primers for cement porous building materials such as mortar, they are not quite satisfactory because the room temperature-curable silicone rubber adhered is easily peeled by immersing the materials in ambient or warm water for a long period of time.
The inventors conducted extensive investigations in an attempt to solve the above-mentioned problems of the conventional primer compositions. As a result, the following phenomenon was found.